Formation fluid sampling method and apparatus



April 7, 1964 J. w. GRAHAM ETAL 3,127,933

FORMATION FLUID SAMPLING METHOD AND APPARATUS FIG.I.

'5 INVENTORS.

JOHN w GRAHAM, NILS L. MUENCH,

ATTORNEY.

April 7, 1964 J. w. GRAHAM ETAL 3,127,933

FORMATION FLUID SAMPLING METHOD AND APPARATUS 2 Sheets-Sheet 2 Filed Sept. 26, 1960 INVENTORS. JOHN W. GRAHAM,

F I G. 6.

z zpwrl/ F IG MUENCH,

NILS L.

ATTORNEY.

United States Patent 3,127,933 FORMATIQN FL UED SAMPLING METHQD AND APPARATUS John W. Graham, Bellaire, Tern, and Niis L. Mueuch,

Huntsville, Ala, assignors, by rnesue assignments, to

Jersey Production Research Company, Tulsa, Okla, a

corporation of Delaware Filed Sept. 26, 1966, flier. No. 58,262 12 Claims. (til. 166-6) The present invention relates to method and apparatus for obtaining samples of subsurface formation fluids.

Techniques commonly used for locating or detecting subsurface oil and gas formations, including well logging, core sampling, drill stem testing, and mud logging, are not entirely satisfactory, primarily because they are expensive and unreliable.

An uncontaminated sample of the formation fluids taken at the time the formation is penetrated by the drill bit would be a desirable method for obtaining a reliable indication of the presence of oil or gas-containing subsurface formations. However, this procedure is not without difficulties, because during the drilling process it is necessary to maintain control of the well, and for that, the hydrostatic pressure of the drilling mud must be greater than the formation pressure at any given depth. Although this pressure differential insures maintenance of control during the drilling operation, it also prevents oil or gas from flowing into the borehole from the formation even though a potentially valuable oil or gas Zone may be penetrated by the drill bit.

The present invention overcomes this difficulty and permits obtaining a sample of the formation fluids at the time the formation is penetrated by the drill bit.

In essence, the invention involves drawing a sample of formation fluids into the borehole adjacent the drill bit by raising the drill pipe while restricting the downward flow of drilling mud in the annulus between the drill pipe and borehole wall; and then reverse circulating to the earths surface the sample of formation fluids swabbed into the well bore.

The apparatus in one embodiment of the invention ineludes a partially expansible packer sub means located in the drill pipe adjacent to the drill bit; a rabbet trap or fluid flow diverting means located in the drill pipe adjacent the surface of the earth; and a rabbet device adapted to be moved up and down the drill pipe by circulating fluids. This apparatus is used to obtain a sample of formation fluids by pumping the rabbet device down the drill pipe to the packer sub means where it lodges and blocks the flow passage through the drill pipe to permit fluid pressure to partially expand the expansible element of the packer sub means; raising the drill pipe at a rate sufficient to reduce pressure below the drill bit to less than the formation pressure to permit formation fluids to flow into the borehole, and then reverse circulating drilling mud down the drill pipe-borehole wall annulus to collapse the expansible packer element (after which the drill pipe is preferably lowered to its original position) and to force the rabbet device upward through the drill pipe until it lodges in and actuates the rabbet trap or fluid-flow diverting means to cause the sample of formation fluids following the rabbet device to be diverted to a sampler container.

In another embodiment of the invention, a viscous mud slug instead of the partially expansible packer sub means is used to restrict the flow of drilling mud in the drill pipeborehole wall annulus when the drill pipe and drill bit are raised. The viscous mud slug is pumped down the drill pipe and up the drill pipe-borehole wall annulus ahead of a rabbet device which lodges in the drill bit or lower "ice end of the drill collar to block passage of fluid flow through the drill bit and prevent further fluid circulation. The volume of the viscous mud slug may be suitably that suflicient for the mud column formed in the annulus to extend the length of the drill collars. After the viscous mud slug is located in the annulus, the drill pipe is raised at a rate sufficient to reduce pressure below the drill bit to less than the formation pressure to draw formation fluids into the borehole (after which the drill pipe is preferably lowered to its original position). Drilling mud then is reverse circulated down the annulus to displace the viscous mud, sample of formation fluids and rabbet device upwardly to the surface. The fluid flow diverting means diverts the sample of formation fluids to a sampler container.

If desired, the two embodiments of the invention may be used in conjunction with one another; that is, both the partially expansible packer sub means and the viscous mud slug may be used together.

Thus, a primary object of the present invention is to provide improved apparatus and method for sampling subsurface formation fluids during drilling operations.

The above object and other objects of the invention will be apparent from a more detailed description thereof taken in conjunction with the drawings wherein:

FIG. 1 is a cross-sectional View of the earths subsurface showing a drill pipe arranged in a borehole and a derrick and associated drilling equipment arranged on the earths surface.

FIG. 2 is a cross-sectional view of a portion of the earths subsurface showing the drill bit raised olf bottom of the borehole and the expansible element of the packer sub in its partially inflated position;

FIG. 3 is a vertical, partly-sectional view showing the packer sub in greater detail with the parts thereof arranged in the normal drilling position;

FIG. 4 is a view similar to that shown in FIG. 3 showing the packer sub parts in sample-taking position;

FIG. 5 is a vertical, partly-sectional view showing the upper fluid flow diverting apparatus in normal drilling position; and

FIG. 6 is a view similar to that shown in FIG. 5 showing the fluid flow diverting apparatus in sample-taking position.

Referring to the drawings in greater detail, in FIG. 1 is shown a borehole 10 penetrating the earth and in which is arranged a drill string 11, to the lower end of which is attached a drill bit 12. A packer sub 13 located ad jaeent drill bit 12 is connected in a drill collar 14, the upper end of which is connected to the lowermost drill pipe sec tion. On the earths surface is arranged surface drilling equipment including a derrick 16, a mud pit 17 and a mud pump 18. A standpipe 19 to which is connected a hose 20, and which, in turn, connects to the swivel 21 and Kelly 22, is attached to mud pump 18. The lower end of Kelly 22 connects to a special joint 23, which connects at its lower end to the uppermost section of drill string 11. A sampler hose 24 interconnects special joint 23 and a sampler container 25. Wellhead 26 includes blowout preventers 27. A conduit 28 interconnects wellhead 26 and mud pit 17 for fluidly communicating the mud pit and the annulus between the drill string and the well bore wall. Another conduit 29 fluidly communicates standpipe 19 and conduit 28. Another valved conduit 19 interconnects standpipe 19 and mud pit 17.

In FIG. 2, the drill pipe string has been raised until drill bit 12 is off bottom. Expansible packer element 30 of packer sub 13 has been partially inflated, and fluids from a formation A, penetrated by drill bit 12, are flowing into the well bore below the bit as indicated by the arrows.

FIGS. 3 and 4 show the partially inflatable packer sub means 13 in detail. It comprises a mandrel 31 connected in drill collar 14 and provided with a bore 32, having an enlarged portion 33, and an opening or passageway 34 fluidly communicating portion 33 of bore 32 and the exter-ior of the mandrel; a slidable sleeve valve 35 arranged in enlarged portion 33 of bore 32 adjacent passageway 34 functions to open and close the interior end thereof; a spring 36 seated in the enlarged portion 33 below valve 35 biases the valve upwardly to the passageway closed position; and upper and lower recesses 37 and 38, respectively, having arranged therein movable rods 39 which extend to the exterior of mandrel 31 and connect to expansible packer element 30, which surrounds passageway 34 as well as the recesses and rods. The elements are shown in normal drilling, packer deflated condition in FIG. 3. In FIG. 4 packer element 30 is inflated for sample taking. A rabbet comprising a ball as is lodged on a seat 41 formed on the lower end of valve 35, which is in its lowermost position, spring 36 is compressed, passageway 34 is opened, and rods 39 are in their extended positions. Since it is conventional practice for the bore 32 of drill collar 14 to be of smaller diameter than the bore 43 of the drill string 11, the rabbet may include a cage 44 of the diameter of the drill string bore 43 and be provided with ring seals 55 on its outer surface for engaging walls of the drill pipe and an inner sleeve 46 for retaining ball 40 during their descent through the drill string.

The special upper joint 23 is shown in detail in FIGS. and 6. The interior surface of the upper end of joint 23 is enlarged to form a recessed portion 5% in which is arranged a rabbet trap in the form of a sleeve valve 51 provided with suitable ring seals 52 on the exterior surface for sealingly engaging the interior wall of the joint. A spring 53 is arranged in recessed portion 5d above valve 51 and functions to bias it downwardly to close off (see FIG. 5) a passageway 54 in joint 23 which fluidly communicates with the sampler hose. In FIG. 6 valve 51 is in its uppermost position, spring 53 is compressed, passageway 54 is open, and the rabbet is seated in the valve; cage 44 is lodged on a seat 55 in the upper end of valve 51, and ball 40 is lodged on seat 56 formed by sleeve 46 at the upper end thereof.

In operation, sub 13 is connected in drill collar 14 and drilling operations are conducted as usual. With inflatable packer element deflated, as illustrated in FIGS. 1 and 3, drilling operations are not aflected by the presence of sub 13.

When a drilling break is obtained, or when for any other reason it is desired to obtain a sample of formation fluids, drill pipe string 11 is broken at the uppermost tool joint, and special joint 23, in which is arranged rabbet 40, 44, is connected to Kelly 22 and the uppermost tool joint. The rabbet is pumped down drill pipe 11, by circulating drilling mud through pump 18, standpipe 19, hose 20, Kelly 22, special joint 23, drill pipe 11, drill collar 14, mandrel 13, drill bit 12, the annulus between the wall of the well bore 1t and drill pipe 11 and conduit 28, to the bottom of the drill pipe where cage 44 engages and is retained by the upper shoulder of drill collar 14. Ball continues to move downwardly until it engages seat 41 of valve 35. Valve 35 then is forced downward against the bias of spring 36. Upon this occurrence, as seen in FIG. 4, opening 34 opens and fluidly communicates the enlarged portion 33 of bore 32 and the exterior of mandrel 31, and fluid pressure passes through opening 34 and inflates packer element 30. However, the amount of inflation of packer element 30 is limited by the distance rods 39 are permitted to move outwardly. This length is designed to prevent packer element 30 from packing olf hard against the wall of the borehole. It is permitted to expand to a prefixed diameter, which is slightly less than borehole diameter, as seen clearly in FIG. 2. As illustrated in this figure, when the packer element 36 has been partially inflated, drill pipe string 11 is raised until drill bit 12 is oif bottom a distance of about 30 to 60 feet. As the drill pipe is withdrawn, fluid in the drill pipe-borehole Wall annulus flows past the small clearance around the packer in order to fill the void space created below the packer caused by withdrawal of the drill pipe. However, if the drill pipe is withdrawn at moderate, selected rates, the fluid is unable to flow past the packer at a suflicient rate to fill the void space created below the packer. In this manner, the pressure is lowered below the packer an amount suflicient to permit formation fluids to flow into the void space, and large samples of formation fluids slightly diluted by drilling mud are drawn into the borehole. Then, reverse circulation of drilling mud through conduit 29, down the borehole-drill pipe string annulus and up drill bit 12, mandrel 31, drill collar 14 and drill pipe 11 is initiated after which drill pipe 11 is lowered to its original position in which drill bit 112 is on bottom. Reverse fluid circulation deflates packer element 36, moves ball 49 upwardly, and the formation fluid sample is circulated to the surface immediately behind the ball. Once ball 40 moves upwardly as it is forced by the circulating mud upwardly, spring 36 moves valve 35 to its uppermost position, which closes olf passageway 34. As ball 49 is forced upwardly, it engages and seats in cage 44, and both members comprising the rabbet are forced upwardly. The circulating mud which is ahead of and above rabbet 40, 44 passes up through special joint 23, and Kelly 22 and down standpipe 19 and conduit 19' to mud pit 17. When rabbet 4t), 44- reaches the rabbet trap or sleeve valve 51 of joint 23, cage 44 lodges in seat 55 in valve 51 and moves it upwardly to its uppermost position, which opens passageway 54 to the interior of drill pipe ill and causes the circulating fluid to be diverted through passageway 54, as indicated by the arrows in FIG. 6. Thus, formation fluids mixed with some amount of drilling mud are automatically diverted for collection and examination and analysis.

When it is desired to continue drilling, special sub 23 is removed and Kelly 22 and the uppermost tool joint are reconnected.

The volume of fluid sample obtainable is calculable and is dependent not only upon the clearance between the packer and the borehole and upon the permeability of the formation, but is also dependent upon the rate of withdrawal of the drill pipe.

The operation of the embodiment of the invention em ploying the viscous mud slug is similar to the operation of the embodiment using the partially expansible packer sub except that a viscous mud slug of sufficient volume to displace fluid in the annulus between the drill pipe and the borehole wall approximately the length of the drill collar is introduced into the drill pipe ahead of the rabbet.

After special joint 23 is connected to Kelly 22 and the uppermost tool joint, a high viscosity mud is pumped into drill pipe 11. This mud, which may be suitably a mud having a high bentonite concentration, may be introduced into and returned from drill pipe 11 through passageway 54- which may be connected to a small storage tank containing the viscous mud, as well as to hose 24 leading to sampler container 25. Rabbet 4-9, 44 is pumped down drill pipe 11 behind the viscous mud slug by circulating drilling mud. Cage 44 is retained by the shoulder of drill collar 14 and ball 40 seats in drill bit 12 and blocks further fluid flow therethrough. The viscous mud slug circulated ahead of ball 40 displaces drilling mud and forms a mud column of sufficient length and of suflicient rigidity in the drill pipe-borehole annulus to generate a swab action when the drill pipe and drill bit are raised. Once the viscous mud column is formed, drill pipe 11 is raised thereby drawing formation fluids into the borehole. Then by reverse circulating fluids down the annulus and up the drill pipe the rabbet, formation fluid sample and viscous mud slug are conducted to the surface. The sample and the viscous mud are diverted to passageway 54 in the same manner as the sample was diverted in the description of the previous embodiment. The sample is conducted to sampler container 25 and the viscous mud slug may be diverted to its storage tank in any desired manner.

The operation is the same when both the mud slug and the partially expansible packer techniques are used together except for the function of the packer sub which would be the same as that previously described.

The invention is advantageous in that it is reliable, inexpensive and quick. The sample obtained is natural formation fluids contaminated with a minimum of mud filtrate. The necessary equipment is simple and reliable. The method may be readily handled by regular personnel, and therefore no delay to obtain special services is involved. The sample is obtained with the drill bit in the hole. Therefore, drilling can be continued following a test and can always be ready for test immediately after any drill break. Another important advantage is that the well is always under control by the circulating fluids; there is never a danger of blowout.

Having fully described the method, apparatus, operation and objects of our invention, we claim:

1. A method for obtaining samples of formation fluids through a drill pipe string during drilling operations comprising the steps of closing oif adjacent the drill bit the circulating fluid flow path downward through the drill pipe string; raising the drill pipe and drill bit while restricting the downward flow of drilling mud in the annulus between the drill pipe string and the borehole wall to reduce pressure below the drill bit to less than formation pressure to thereby draw a sample of formation fluids into the borehole below the drill bit; and reverse circulating fluids down said annulus through the drill bit and up the drill pipe string until the sample of formation fluids reaches the earths surface.

2. A method for obtaining samples of formation fluids through a drill pipe string during drill operations comprising the steps of closing off adjacent the drill bit the circulating fluid flow path downward through the drill pipe string; raising the drill pipe string and drill bit while restricting the downward flow of drilling fluid in the annulus between the drill pipe string and the borehole wall to reduce pressure below the drill bit to less than formation pressure to thereby draw a sample of formation fluids into the borehole below the drill bit; lowering said drill pipe string; and reverse circulating fluids down said annulus through the drill bit and up the drill pipe string until the sample of formation fluids reaches the earths surface.

3. A method for obtaining samples of formation fluids through a drill pipe string comprising the steps of closing off adjacent the drill bit the circulating fluid flow path downward through the drill pipe string; partially closing off the annulus between the borehole wall and the drill pipe string adjacent the drill bit while the drill bit is adjacent the bottom of the borehole; then while maintaining the annulus between the borehole wall and the drill pipe string adjacent the drill bit partially closed oif, raising the drill pipe string and drill bit a selected distance at a rate suflicient to reduce the pressure below the drill bit to below the pressure of the formation penetrated by the drill bit thereby drawing formation fluids into the borehole; lowering said drill pipe string and drill bit; and reverse circulating fluids down the annulus between the drill pipe string and the well bore wall and up the drill pipe string until the sample of formation fluids reach the earths surface.

4. A method for obtaining samples of formation fluids through a drill pipe string containing a partially expansible packer sub means adjacent the drill bit, a fluid flow diverting means adjacent the surface of the earth and a rabbet device adapted to be circulated up and down the drill string, comprising the steps of pumping the rabbet device down the drill pipe string to close off adjacent the drill bit the circulating fluid flow path downward through the drill pipe string and to cause fluids circulated behind the rabbet to partially expand the packer element of the sub means; raising the drill pipe string at a sufficient rate to reduce the pressure below the drill bit to less than formation pressure thereby drawing a sample of formation fluids into the borehole; reverse circulating fluids down the annulus between the drill pipe string and the borehole wall to cause collapse of the packer; continuing fluid reverse circulation thereby pumping the rabbet device upwardly through the drill pipe string until the rabbet device engages the fluid flow diverting means; and diverting the sample of formation fluids to a sampler container.

5. A method for obtaining samples of formation fluids through a drill pipe string containing a fluid flow diverting means adjacent the surface of the earth and a rabbet device adapted to be circulated up and down the drill pipe string comprising the steps of introducing into the drill pipe string a viscous mud slug, said mud slug displacing fluids in the annulus between the drill pipe string and the Well bore wall a selected distance; pumping the rabbet device down the drill pipe string behind the viscous mud slug until the rabbet device lodges adjacent the drill bit and prevents further flow of fluid through the drill bit; raising the drill pipe string at a suflicient rate to reduce the pressure below the drill bit to less than formation pressure thereby drawing a sample of formation fluids into the borehole; lowering said drill pipe string; and reverse circulating fluids down the annulus between the drill pipe string and the borehole wall to reverse circulate the rabbet device, the sample of formation fluids and the viscous mud upwardly through the drill pipe string, the rabbet device engaging the fluid flow diverting means when it reaches the surface to divert the sample of formation fluids flowing behind the rabbet device to a sampler container.

6. A method for obtaining samples of formation fluids through a drill pipe string containing a partially expansible packer sub means adjacent the drill bit, a fluid flow diverting means adjacent the surface of the earth and a rabbet device adapted to be circulated up and down the drill pipe string comprising the steps of introducing a viscous mud slug into the drill pipe string, said mud slug displacing a column of drilling mud in the annulus between the drill pipe string and the borehole wall a selected distance; pumping the rabbit device down the drill pipe string behind the mud slug to close off adjacent the drill bit the circulating fluid flow path downward through the drill pipe string and to cause fluids circulated behind the rabbet device to partially expand the packer element of the sub means and to form a column of said viscous mud in said annulus; raising the drill pipe string at a sufficient rate to reduce the pressure below the drill bit to less than formation pressure thereby drawing formation fluids into the borehole, lowering said drill pipe string; reverse circulating fluids down the annulus between the drill pipe string and the borehole wall to cause collapse of the packer and also to reverse circulate the rabbet device upwardly through the drill pipe string until the rabbet device engages the fluid flow diverting means; and then diverting the sample of formation fluids to a sampler container.

7. A method for obtaining samples of formation fluids through a drill pipe string comprising the steps of closing off adjacent the drill bit the circulating fluid flow path downward through the drill pipe string; partially closing off the annulus between the borehole wall and the drill pipe string adjacent the drill bit while the drill bit is adjacent the bottom of the borehole; then while maintaining the annulus between the borehole wall and the drill pipe string adjacent the drill bit partially closed ofl, raising the drill pipe string and drill bit a selected distance at a rate sufiicient to reduce the pressure below the drill bit to below the pressure of the formation penetrated by the drill bit thereby drawing formation fluids into the borehole; and reverse circulating fluids down the annulus between the drill pipe string and the well bore wall and up 3' the drill pipe string until the sample of formation fluids reaches the earths surface.

8. A method for obtaining samples of formation fluids through a drill pipe string containing a partially expansible packer sub means adjacent the drill bit, a fluid flow diverting means adjacent the surface of the earth and a rabbet device adapted to be circulated up and down the drill string, comprising the steps of pumping the rabbet device down the drill pipe string to close off adjacent the drill bit the circulating fluid flow path downward through the drill pipe string and to cause fluids circulated behind the rabbet to partially expand the packer element of the sub means; raising the drill pipe string at a suflicient rate to reduce the pressure below the drill bit to less than formation pressure thereby drawing a sample of formation fluids into the borehole; reverse circulating fluids down the annulus between the drill pipe string and the borehole wall to cause collapse of the packer; lowering the drill pipe string to its original position; continuing fluid reverse circulation thereby pumping the rabbet device upwardly through the drill pipe string until the rabbet device engages the fluid flow diverting means; and diverting the sample of formation fluids to a sampler container.

9. A method for obtaining samples of formation fluids through a drill pipe string containing a fluid flow diverting means adjacent the surface of the earth and a rabbet device adapted to be circulated up and down the drill pipe string comprising the steps of introducing into the drill pipe string a viscous mud slug, said mud slug displacing fluids in the annulus between the drill pipe string and the well bore wall a selected distance; pumping the rabbet device down the drill pipe string behind the viscous mud slug until the rabbet device lodges adjacent the drill bit and prevents further flow of fluid through the drill bit; raising the drill pipe string at a suflicient rate to reduce the pressure below the drill bit to less than formation pressure thereby drawing a sample of formation fluids into the borehole; reverse circulating fluids down the annulus between the drill pipe string and the borehole wall to reverse circulate the rabbet device, the sample of formation fluids and the viscous mud upwardly through the drill pipe string, the rabbet device engaging the fluid flow diverting means when it reaches the surface to divert the sample of formation fluids flowing behind the rabbet device to a sampler container.

10. A method for obtaining samples of formation fluids through a drill pipe string containing a partially expansible packer sub means adjacent the drill bit, a fluid flow diverting means adjacent the surface of the earth and a rabbet device adapted to be circulated up and down the drill pipe string, comprising the steps of introducing a viscous mud slug into the drill pipe string, said mud slug displacing a column of drilling mud in the annulus between the drill pipe string and the borehole wall a selected distance; pumping the rabbet device down the drill pipe string behind the mud slug to close off adjacent the drill bit the circulating fluid flow path downward through the drill pipe string and to cause fluids circulated behind the rabbet device to partially expand the packer element of the sub means and to form a column of said viscous mud in said annulus; raising the drill pipe string at a sufficient rate to reduce the pressure below the drill bit to less than formation pressure thereby drawing formation fluids into the borehole; reverse circulating fluids down the annulus between the drill pipe string and the borehole wall to cause collapse of the packer, and also to reverse circulate the rabbet device upwardly through the drill pipe string until the rabbet device engages the fluid flow diverting means; and then diverting the sample of formation fluids to a sampler container.

11. Apparatus for obtaining samples of formation fluids during drilling of a borehole with a drill pipe string provided with a drill bit on the lower end thereof comprising an expansible packer located in said drill pipe adjacent said drill bit including means to limit expansion of said packer to close off only partially the annulus between said drill pipe string and the borehole wall; a rabbet device adapted to be circulated down and reverse circulated up the drill pipe string; valve means located in said drill pipe string adjacent said drill bit adapted to close off downward drilling fluid circulation through said drill pipe string and to permit drilling fluids to expand said packer when engaged by said rabbet device upon downward circulation thereof down said drill pipe string; and a fluid flow diverting means located in said drill pipe string adjacent the surface of the earth adapted to divert a reverse circulated sample of formation fluids to a sampler container when it is actuated by said rabbet device upon reverse circulation thereof up said drill pipe string.

12. Apparatus for obtaining samples of formation fluids during drilling of a borehole with a drill pipe string provided with a drill bit on the lower end thereof comprising:

a packer located in said drill pipe adjacent said drill bit including means to limit expansion of said packer to close off only partially the annulus between said drill pipe string and the borehole wall;

a rabbet device adapted to be circulated down and reverse circulated up the pipe string;

first valve means located in said drill pipe string adjacent said drill bit adapted to close off downward drilling fluid circulation through said drill pipe string and to permit drilling fluids to expand said packer when engaged by said rabbet device upon downward circulation thereof down said drill pipe string; and

fluid flow diverting means located in said drill pipe string adjacent the surface of the earth including a passageway through which fluid flowing upwardly through said drill pipe string may be diverted and second valve means adapted to close ofl? said passageway when in one position and to open said passageway to divert a reverse circulated sample of formation fluids to a sampler container when in a second position, said second valve means being moved from said one to said second position by said rabbet device upon reverse circulation thereof up said drill pipe string.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A METHOD FOR OBTAINING SAMPLES OF FORMATION FLUIDS THROUGH A DRILL PIPE STRING DURING DRILLING OPERATIONS COMPRISING THE STEPS OF CLOSING OFF ADJACENT THE DRILL BIT THE CIRCULATING FLUID FLOW PATH DOWNWARD THROUGH THE DRILL PIPE STRING; RAISING THE DRILL PIPE AND DRILL BIT WHILE RESTRICTING THE DOWNWARD FLOW OF DRILLING MUD IN THE ANNULUS BETWEEN THE DRILL PIPE STRING AND THE BOREHOLE WALL TO REDUCE PRESSURE BELOW THE DRILL BIT TO LESS THAN FORMATION PRESSURE TO THEREBY DRAW A SAMPLE OF FORMATION FLUIDS INTO THE BOREHOLE BELOW THE DRILL BIT; AND REVERSE CIRCULATING FLUIDS DOWN SAID ANNULUS THROUGH THE DRILL BIT AND UP THE DRILL PIPE STRING UNTIL THE SAMPLE OF FORMATION FLUIDS REACHES THE EARTH''S SURFACE. 